1. Field of the Invention
The present invention relates to a method and apparatus for forming colloidal photonic crystals, and more particularly, to a method and apparatus for forming colloidal photonic crystals on a flexible substrate.
2. Description of the Related Art
Photonic crystals have periodic structures in which various materials having sizes of several hundred nanometers to several micrometers are arranged in one, two, or three dimensions. Photonic crystals can be manufactured using a photolithography technique, a micro-electro mechanical system (“MEMS”) technique, or a colloidal self-assembly technique.
Photonic crystals reflect visible light having a predetermined wavelength among the various wavelengths of white light, and are applied in various fields. In detail, the colloidal photonic crystals can be applied to various systems that require an optical filter. For example, colloidal photonic crystals reflecting visible light corresponding to red, green, or blue wavelengths among the various wavelengths of white light can be used as color filters of a reflective display device. In addition to this optical application, since colloidal photonic crystals have a structure in which monodisperse colloidal particles are regularly self-assembled, when surfaces of the colloidal particles that form colloidal photonic crystals are doped with a catalyst material, the colloidal particles can be used as catalyst supports. Also, since the wavelength of light reflected by the colloidal photonic crystals changes according to the angle of incidence of white light on the colloidal photonic crystals, the color changes according to angles from which the observer is looking. Accordingly, the colloidal photonic crystals can also be used in cosmetic products, e.g., for nails or faces.
In the conventional art, colloidal photonic crystals are manufactured by coating a colloidal solution, in which colloidal particles are dispersed, on a flat substrate, and then evaporating a solvent to self-assemble the colloidal particles voluntarily, or by using a dip coating method in which the substrate is dipped in the colloidal solution and then removed very slowly to evaporate the solvent, thereby forming photonic crystals. However, these methods require long times for evaporation of the solvent, and it is difficult to produce photonic crystals on large surfaces using these methods. In a known method for solving these above problem, a high-density colloidal solution, in which colloidal particles are condensed, is injected between two flat substrates spaced apart from each other. Then, a shear stress is applied to the colloidal solution using relative vibration of the two flat substrates, thereby self-assembling colloidal particles. However, this method requires a spacer to maintain a predetermined distance between the two flat substrates between which the colloidal solution is injected. In addition, some of the photonic crystals may be damaged when removing the flat substrates after the colloidal photonic crystals are formed.